As the means for synchronously operating a plurality of cameras connected to a serial bus such as IEEE 1394 or USB 3.0, conventionally, there are a structure in which a synchronization signal generation means is provided outside the cameras, and a structure in which a synchronization signal generation means is embedded within the cameras.
In a structure in which the synchronization signal generation means is provided outside the cameras, separately from bus connection by means of a serial bus, a synchronization signal generator, and a dedicated signal line for synchronization which supplies a synchronization signal output from the synchronization signal generator to each of the cameras are provided externally. By supplying a synchronization signal output from the synchronization signal generator to each of the cameras via the dedicated signal line for synchronization, synchronous control is performed for each of the cameras connected to the serial bus.
Further, in a structure in which the synchronization signal generation means is embedded in each of the cameras, a synchronization signal generation circuit for realizing synchronization between the cameras is provided in each camera connected to the serial bus. The synchronization signal generation circuit embedded in each camera generates a synchronization signal by using a specific packet over the serial bus.
Of the above-described structures, a system structure in which a synchronization signal generation means is provided outside the cameras has a problem that the structure of the whole system becomes complicated since this structure requires a synchronization signal generator to be provided externally, separately from the camera connection structure via the serial bus, and a synchronization signal output from such a synchronization signal generator is supplied to each camera through a dedicated signal line for synchronization. Further, in the structure in which the synchronization signal generation means is embedded in each camera, a synchronization signal generator embedded in each camera generates a synchronization signal by using a value of a specific packet issued from another apparatus on the control side and a signal of predetermined intervals generated within the camera. For this reason, this structure has a problem that the structure of a synchronization control circuit within the camera becomes complicated.
Accordingly, the applicant of the present application has realized a synchronous camera capable of easily constructing a camera system which synchronously controls a plurality of cameras over the IEEE 1394 bus with an economically advantageous structure.
The synchronous camera as described above has the feature that a system structure for synchronization and the structure within the camera can be simplified, and that the camera system which synchronously controls a plurality of cameras over the IEEE 1394 bus is thereby easily constructed with an economically advantageous structure. However, the aforementioned structure causes a problem that a certain level of reliability cannot be ensured for other high-speed serial bus interfaces (for example, a USB 3.0 serial bus interface) which allow greater fluctuation in packet arrival time as compared to synchronous control over the IEEE 1394 bus.
The embodiment has been achieved in light of the above points, and is intended to provide a synchronous camera which can easily construct a camera system capable of performing highly reliable synchronous control between cameras, which is targeted for several kinds of high-speed serial bus including USB 3.0, with an economically advantageous structure.